The present invention relates to reaction chambers used for processing semiconductor substrates, such as integrated circuit wafers, and specifically to improvements in the gas distribution system used in these reaction chambers.
Semiconductor processing includes deposition processes such as chemical vapor deposition (CVD) of metal, dielectric and semiconducting materials, etching of such layers, ashing of photoresist masking layers, etc. Such semiconductor processes are typically carried out in vacuum chambers wherein process gas is used to treat a substrate such as a semiconductor wafer, flat panel display substrate, etc. The process gas can be supplied to the interior of the vacuum chamber by a gas distribution system such as a showerhead, a gas distribution ring, gas injectors, etc. Reactors having plural gas distribution systems are disclosed in U.S. Pat. Nos. 5,134,965; 5,415,728; 5,522,934; 5,614,055; 5,772,771; 6,013,155; and 6,042,687.
In the case of etching, plasma etching is conventionally used to etch metal, dielectric and semiconducting materials. A plasma etch reactor typically includes a pedestal supporting the silicon wafer on a bottom electrode, an energy source which energizes process gas into a plasma state, and a process gas source supplying process gas to the chamber.
A common requirement in integrated circuit fabrication is the etching of openings such as contacts and vias in dielectric materials. The dielectric materials include doped silicon oxide such as fluorinated silicon oxide (FSG), undoped silicon oxide such as silicon dioxide, silicate glasses such as boron phosphate silicate glass (BPSG) and phosphate silicate glass (PSG), doped or undoped thermally grown silicon oxide, doped or undoped TEOS deposited silicon oxide, etc. The dielectric dopants include boron, phosphorus and/or arsenic. The dielectric can overlie a conductive or semiconductive layer such as polycrystalline silicon, metals such as aluminum, copper, titanium, tungsten, molybdenum or alloys thereof, nitrides such as titanium nitride, metal silicides such as titanium silicide, cobalt silicide, tungsten silicide, molybdenum silicide, etc. A plasma etching technique, wherein a parallel plate plasma reactor is used for etching openings in silicon oxide, is disclosed in U.S. Pat. No. 5,013,398.
U.S. Pat. No. 5,736,457 describes single and dual xe2x80x9cdamascenexe2x80x9d metallization processes. In the xe2x80x9csingle damascenexe2x80x9d approach, vias and conductors are formed in separate steps wherein a metallization pattern for either conductors or vias is etched into a dielectric layer, a metal layer is filled into the etched grooves or via holes in the dielectric layer, and the excess metal is removed by chemical mechanical planarization (CMP) or by an etch back process. In the xe2x80x9cdual damascenexe2x80x9d approach, the metallization patterns for the vias and conductors are etched in a dielectric layer and the etched grooves and via openings are filled with metal in a single metal filling and excess metal removal process.
It is desirable to evenly distribute the plasma over the surface of the wafer in order to obtain uniform etching rates over the entire surface of the wafer. Current gas distribution chamber designs include multiple supply lines and multiple mass flow controllers (MFCs) feeding separate regions in the chamber. However, the current gas distribution designs require numerous components, complexity in design and high cost. It therefore would be desirable to reduce the complexity and cost to manufacture such gas distribution arrangements.
The present invention provides a gas distribution system useful for a reaction chamber used in semiconductor substrate processing, comprising a plurality of gas supplies, a mixing manifold wherein gas from the plurality of gas supplies is mixed together, a plurality of gas supply lines delivering the mixed gas to different zones in the chamber, the gas supply lines including a first gas supply line delivering the mixed gas to a first zone in the chamber and a second gas supply line delivering the mixed gas to a second zone in the chamber, at least one control valve controlling a rate of flow of the mixed gas in the first and/or second gas supply line such that a desired ratio of flow rates of the mixed gas is achieved in the first and second gas supply lines, at least one flow measurement device measuring flow rate of the mixed gas in the first and/or second gas supply line, and a controller operating the at least one control valve in response to the flow rate measured by the at least one flow measurement device.
According to a preferred embodiment, the controller comprises a computer or programmable logic device which operates the at least one control valve such that a proportion of mixed gas delivered to at least one of the plurality of gas supply lines is changed from a first setpoint to a second setpoint during processing of a semiconductor substrate in the chamber. In one embodiment, the at least one control valve comprises first and second control valves and the at least one flow measurement device comprises first and second flow measurement devices, the first control valve and the first measurement device being located along the first gas supply line and the second control valve and the second flow measurement device being located along the second gas supply line. In another embodiment, the at least one control valve comprises a single control valve and the at least one flow measurement device comprises a single flow measurement device located along either the first or second gas supply line. The reaction chamber can comprise a vacuum chamber such as a plasma etch chamber or a CVD chamber.
The invention also provides a method of processing a substrate in the reaction chamber, the process comprising supplying a semiconductor substrate to the reaction chamber, measuring flow rate of mixed gas in the first and/or second gas supply line with at least one flow measurement device, and processing the substrate by supplying the mixed gas to the first and second zones, the at least one control valve being adjusted by the controller in response to the flow rate measured by the at least one flow measurement device. In a preferred embodiment, the controller monitors total gas flow supplied by the gas supplies to the mixing manifold and compares the total gas flow and the measured gas flow in one of the gas supply lines to a target flow for the second gas supply line, the at least one control valve being repeatedly adjusted by the controller to achieve the desired ratio of flow rates in the first and second gas supply lines. The semiconductor substrate can comprise a silicon wafer which is processed by depositing a layer of material on the wafer or plasma etching a dielectric, semiconductive or conductive layer of material on the wafer.